1. Field of the Invention
The invention relates generally to a method and composition for the treatment of contact lenses. More particularly the invention relates to a method for the treatment of soft contact lenses to remove inorganic deposits on the lenses.
2. Background of the Prior Art
Soft contact lenses may be divided into two broad categories, namely hydrophilic and hydrophobic lenses. Hydrophobic contact lenses are usually based on elastic and flexible silicon rubber (polysiloxane), and are generally made from cross-linking dimethyl polysiloxane. Hydrophilic soft contact lenses are hydrated gel lenses which can be prepared by copolymerizing hydrophilic organic monomers containing an olefinic double bond with a small amount of a cross-linking agent which usually contains two polymerizable olefinic double bonds.
A typical preparation of a silicone contact len is disclosed in U.S. Pat. No. 3,228,741, which is hereby incorporated by reference and comprises forming a mixture of a suitable polymerization catalyst, up to 40% of a silica filler, and the silicone polymer. Said mixture is then molded and cured by heating to cross-link the polysiloxane and to produce a finished clear lens. Increased consumer acceptance of flexible silicone rubber lenses has created a need for a cleaning solution which can be used effectively with such lenses.
Hydrophilic soft contact lenses are usually based on polyhydroxylated alkyl methacrylates and contain a polyhydroxylated alkyl methacrylate, such as polyhydroxyethyl methacrylate (HEMA), cross-linked with, for example, an hydroxyethyl dimethacrylate.
One of the problems connected with these types of lenses is the formation, over a period of time, of insoluble inorganic deposits on the lenses. These deposits are thought to be primarily calcium based, e.g., calcium phosphate and calcium carbonate, but may also contain other inorganic materials and associated organic materials, e.g., protein. The presence of these insoluble inorganic deposits is a common cause of lens intolerance and decreased visual acuity.
U.S. Pat. No. 3,908,680 to Krezanoski discloses a soft contact lens cleaning system involving the cleaning of soft contact lenses by successive immersion in two aqueous solutions, with each solution containing a bleaching agent and preferably a chelating agent. The chelating agents are described by Krezanoski as water softening agents used to tie up divalent and trivalent cations, such as calcium, iron, mercury ions and the like, present in water, thereby preventing undesirable precipitates from forming and ultimately fogging the surface of the lenses.
U.S. Pat. No. 2,547,653 to Minnis, et al, discloses an aqueous solution useful in increasing the comfort of conventional hard contact lenses. The solution contains a small amount, e.g. 2-500 parts per million of a condensed phosphate such as sodium hexametaphosphate.